We have a '97 discovery in the shop and its just plagued with problems. it does not run correctly. at first we thought it was the ignition coil, behind the engine. it doesnt have a distributor cap. we replaced the coil and the problem still persisted, then we tested the sparks with the new coils on, the spark plugs are getting too much power and random repetitions.

after that we turned to the computer which has 3 input connectors. we ordered an used one from another store and plugged it in. this time it did not even start the car, the starter turns funny and pauses between starts.

we've got no idea whats wrong with it, has anyone here experienced the same thing?

 

Pretty vague description of what the initial problem is. What was the problem that made you think to replace the coil pack?

 

These trucks use wasted spark ignition, they fire on the exhaust and compression stroke. The ECM uses one large 40 pin connector.

Can you be more specific on the box location that you changed out. The ECM is between the windshield washer tank and inner fender. What are the DTC's?

 

Would look at crank shaft positon sensor (CKP), driver side rear of engine. Signals ECU and controls timing of spark. BTW, on the non-distibutor trucks, the ECU can set a separate advance for each plug, based on knock sensor and other inputs.

 

misfire on all cylinders, car stalls often, starts very rough, dies when idle gets too low.

 

we changed out the ECM between the windshield washer tank and the inner fender. we ordered another one (it was used) and it didnt even start the LR.
there were no faults present.

 

cps has already been replaced, it did not fix the problem.

 

On these trucks there is a CPS (cam position sensor, front cover) and a crank position sensor (left rear of block) that in the manual is usually called the CKP. The sensor mount uses some spacers, and if they get jiggered during reassembly the spacing of the tip of the sensor is off, and truck won't run or run right. Attached shop manual pages (from a D2, but voltage and concepts are same). If you peer up inside the inspection plate you should be able to see the tabs for the reluctor disk (stamped metal, sometimes a tab is bent or broken. If missing, the ECU gets the count mixed up and fires plugs wrong. One owner posted about braising a missing tab back on without removing tranny (good welder). Tabs are 6 degrees apart, with missing tabs for sync position.

 

The ECM in most cases needs to be married with their companion AS10 alarm boxes. They are tied to one another by the VIN. My 97 would not fire either without the AS10 from the donor vehicle. YMMV but I'm sure that explains why it wouldn't kick.

As for the Crank Position Sensor it's not always the sensor but the wires. They loose their insulation because so near the exhaust. Check for missing insulation and wires touching each other or block. Ran through a stream of this problem about four years ago on another forum and it gave very erratic DTC's and timing issues galore. As far as idle that would be the IAC - Idle Air Control solenoid and it's port full of carbon. Clean it and you'll get a decent idle back.

 

First off, is this your first efforts on a 97 LR Discovery? Sounds like it to me. All 96 and up are missing the distributor as it was the major change after 1995 (3.9). 96 and up are 4.0 in the North American version. And they are obdII compliant. And have the security system that disables the spark and fuel supply when tripped.

The replacement ecm is most likely the cause of the not starting like is indicated above, so I would replace it with the original and then restart your fault isolation process.

I assume the check engine light was on with all those problems. What codes did you read? That is your starting point.

Also the early 97's are GEMS, while later 97 are Bosch.

How many miles on it? What lead you to believe it was the coil pack? The old one is probably still good.

It could easily be as simple as the O2 sensors are shot, giving the wrong info to the ecm, it may need a complete tuneup with new 8mm or good quality wires and new plugs if those are not recent.

It could also be a multitude of minor defects all in conjunction with one another, multiple vacumn leaks, clogged up IACV, and/or dirty MAF Sensor. One thig that ade a significant difference in mine was a thorough cleaning of all the ports on the plenum.

Do you have the reference material for the vehicle? It is a free download in Savannah's signature above.

Hope you figure out how to figure it out.